进程间同步

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互斥量mutex

进程间也可以使用互斥锁，来达到同步的目的。但应在pthread_mutex_init初始化之前，修改其属性为进程间共享。

mutex的属性修改函数主要有以下几个。

主要应用函数：

pthread_mutexattr_t mattr 类型：用于定义mutex锁的【属性】

pthread_mutexattr_init函数：初始化一个mutex属性对象

int pthread_mutexattr_init(pthread_mutexattr_t*attr);

pthread_mutexattr_destroy函数：销毁mutex属性对象 (而非销毁锁)

int pthread_mutexattr_destroy(pthread_mutexattr_t *attr);

pthread_mutexattr_setpshared函数：修改mutex属性。

intpthread_mutexattr_setpshared(pthread_mutexattr_t *attr, int pshared);

参2：pshared取值：

线程锁：PTHREAD_PROCESS_PRIVATE(mutex的默认属性即为线程锁，进程间私有)

进程锁：PTHREAD_PROCESS_SHARED

进程间mutex示例

#include <stdio.h>
#include <unistd.h>
#include <fcntl.h>
#include <stdlib.h>
#include <string.h>
#include <pthread.h>
#include <sys/mman.h>
#include <sys/wait.h>

struct mt {
int num;
pthread_mutex_t mutex;
pthread_mutexattr_t mutexattr;
};

int main(void)
{
int i;
struct mt *mm;
pid_t pid;
/*
int fd = open("mt_test", O_CREAT | O_RDWR, 0777);
ftruncate(fd, sizeof(*mm));
mm = mmap(NULL, sizeof(*mm), PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0);
close(fd);
unlink("mt_test");
*/
mm = mmap(NULL, sizeof(*mm), PROT_READ|PROT_WRITE, MAP_SHARED|MAP_ANON, -1, 0);
memset(mm, 0, sizeof(*mm));

pthread_mutexattr_init(&mm->mutexattr); //初始化mutex属性对象
pthread_mutexattr_setpshared(&mm->mutexattr, PTHREAD_PROCESS_SHARED); //修改属性为进程间共享

pthread_mutex_init(&mm->mutex, &mm->mutexattr); //初始化一把mutex琐

pid = fork();
if (pid == 0) {
for (i = 0; i < 10; i++) {
pthread_mutex_lock(&mm->mutex);
(mm->num)++;
pthread_mutex_unlock(&mm->mutex);
printf("-child----------num++ %d\n", mm->num);
}
} else if (pid > 0) {
for ( i = 0; i < 10; i++) {
// sleep(1);
pthread_mutex_lock(&mm->mutex);
mm->num += 2;
pthread_mutex_unlock(&mm->mutex);
printf("-------parent---num+=2 %d\n", mm->num);
}
wait(NULL);
}

pthread_mutexattr_destroy(&mm->mutexattr); //销毁mutex属性对象
pthread_mutex_destroy(&mm->mutex); //销毁mutex
munmap(mm,sizeof(*mm)); //释放映射区

return 0;
}

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